Two divergent views have been held as to the nature of the original hexapod stock.
Scorpio is here provided with a single or double pair of renal excretory tubes, which have been identified by earlier authors with the Malpighian tubes of the Hexapod and Myriapod insects.
An adult Hexapod is provided with a firm, well-chitinized cuticle and six conspicuous jointed legs.
The fat-body is therefore the seat of important metabolic processes in the hexapod body.
That portion of the gut which is formed by the hypoblast, whereas in Hexapod insects the similar caecal tubes are developed from the proctodaeum or in -pushed portion of the gut which is formed from epiblast.
Taken in connexion with the likeness of the young among the more generalized orders to the adults, it indicates clearly a thysanuroid starting-point for the evolution of the hexapod orders.
The history of the development of the head has been carefully worked out in the Hexapod insects.
Toothed so as to act as a biting jaw in the Hexapod Mantis, the Crustacean Squilla and others); with the last joint produced into a needle-like stabbing process in spiders.
The number is significant, since it agrees with that found in Edriophthalmous Crustacea, and assigns the labium of the Hexapod to the same somite numerically as that which carries the labium-like maxillipedes of those Crustacea.